In separating or removing a certain substance from a liquid by using a filter that does not let the liquid pass easily therethrough, it is a common practice to use a centrifuge. To process a liquid by the centrifuge, a sample holding container has been in common use which is generally cylindrical and comprises a vial-engaging opening portion at a lower end thereof engageable with an opening portion of a filtered product accommodating glass vial, a sample-introducing opening portion at an upper end thereof into which a sample liquid to be filtered is introduced, a filter provided between the vial-engaging opening portion and the sample-introducing opening portion to separate them from each other, and a cover to hermetically close the sample-introducing opening portion.
To filtrate a biological substance using the sample holding container, the following steps are taken. First, the sample liquid is introduced from the sample-introducing opening portion into a space on the sample-introducing opening portion side of the filter and then the sample-introducing opening portion is closed with the cover. Then, the vial-engaging opening portion is fitted into the opening portion of the glass vial to form an assembly. Next, the sample holding container assembly is mounted in the centrifuge so that the filter is situated on the far side from the sample-introducing opening portion with respect a rotating axis of the centrifuge, with a vertical axis of the container assembly extending in a rotating radial direction perpendicular to the rotary axis of the centrifuge. To strike a balance, another sample holding container assembly is mounted on the opposite side of the rotating axis. Then, the centrifuge is rotated. As a result, the sample liquid that is forced through the filter is received in the glass vials (non-patent document 1).
Non-patent document 1: “MICROCON Centrifugal Filter Devices User Guide” (published by Millipore Corporation, 2000).
The use of a centrifuge that is required in performing filtration using a filter through which a liquid cannot easily pass has a problem of expanding the overall size of the equipment. There is another problem that installing the sample holding container assemblies in the centrifuge can only be done manually, making it difficult to automate a series of operations including preprocessing. Further, a control on the centrifuge can only be performed mainly in terms of only a revolution speed, leaving a fine control impossible. Still another problem is that an appropriate centrifugal force needs to be set according to liquid volumes and filter pore diameters, making the equipment difficult to handle.
It is therefore a first object of this invention to provide a filtration method, a filter-incorporated tip and a filtration device which can perform a process including a filtration with a simple construction without having to expand a size of the device.
A second object is to provide a filtration method, a filter-incorporated tip and a filtration device which can automate an entire series of operations for a process using a filter.
A third object is to provide a filtration method, a filter-incorporated tip and a filtration device which can perform a finely and optimally adjusted process according to a filter used and a liquid being processed.